Also, it's possible that:
#. 110503$1x
|out of memory
| #.110503$1
You can use a folding instead:
([++:@])/ 110503$1x
5219283133417550597608921138394131714748003987...
or ignoring the 1s:
>:@+:@]/ 110503$1x
or with power ^:
>:@+:^: (<: 110503) 1x
5219283133417550597608921138394131714748003987...
but it's also very slow..
ts '([++:@])/ 110503$1x'
16.633282 788352
ts '>:@+:^: (110502) 1x'
16.738218 329344
Using a specialized exponentiation provides some speed up:
powGB=: (**:)/@(|....@#:@]{1x,[) NB. don't know who's brainchild, sorry
... and showing the last 31 digits:
ts 'it=:_31{.": <: 2x powGB 110503'
0.633862 296960
it
9131999107769951621083465515007
Compared to:
ts 'it=:_31{.": <: 2x ^ 110503'
1.414242 430912
it
9131999107769951621083465515007
I didn't try MP39 though (well, just for a while). :-)
To obtain MP39 I used Haskell's interpreter GHCi (using the equivalence
of ext. prec.: arbitrary prec. integers) showing the last 46 digits from
a total of 4053946 digits ( >.13466917*10^.2) :
*Main> (take 9 &&& (take 9 .drop 4053937)).show . pred $ 2^13466917
("924947738","256259071")
(19.89 secs, 155769356 bytes)
Check with: http://en.wikipedia.org/wiki/Mersenne_prime
Hallo Matthew Brand, je schreef op 08-04-09 09:09:
> You can do it like this:
> #. N # 1x
>
> ... but it is *much* slower than doing <: 2x^N
>
> On Tue, Apr 7, 2009 at 7:39 PM, <[email protected]> wrote:
>
>> The following are Mersenne Primes 2, 3, 15, 29 and 39
>>
>> MP2 =: <:2x^3
>> MP3 =: <: 2x^5
>> MP5 =: <: 2x^13
>> MP15 =: <: 2x^1279
>> MP29 =: <: 2x^110503
>> MP39 =: <: 2x^13466917
>>
>> As an example <: 2x^3 in binary is 1000 - 1 which is binary
>> 111
>>
>> Any mersenne prime of the form <: 2x^N is "N binary 1s"
>>
>> It takes a very long time to calculate MP39.
>>
>> How could I accomplish the same thing by noting that in the
>> case of MP39, I need to create an
>> extended value that is "13466917 binary 1s"
>>
>> thanks
>>
>>
>>
>>
>> ----------------------------------------------------------------------
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>>
>>
>
>
>
>
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